1. Field of the Invention
This invention relates to video display systems. More particularly, the present invention is directed to a method and apparatus to convert a source image to a destination image, and is directed to a method and apparatus to produce video signal timing to a display apparatus that has an output/display video format different from an input video format.
2. Description of the Prior Art
There are numerous kinds of interlaced video signals such as NTSC and PAL, and progressive scan video signals such as VESA VGA, SVGA, XGA, and SXGA. Several methodologies have been adopted in the prior art method in order to accommodate different types of source video signals for viewing on a single display apparatus. And the prior art method involves converting resolution and the frame rate of source video signals which usually include a plurality of image frames/fields to a format which is supported by the display apparatus, such as LCDs, plasma display panels (PDPs), and TV sets.
In the display apparatus, there are usually a controller and a display screen, such as a flat panel display and a CRT monitor. The controller is provided for performing necessary video format conversion and related controlling functions. The buffer is provided for receiving and temporarily storing the source video signals. The display apparatus receives the image frames at an input frame rate, and outputs at an output frame rate after performing necessary video format conversion.
If the input and output frame or field rates do not match each other, the data transferred for displaying the output images will overflow or underflow in the buffer. Then, the picture displayed will come from two different frames. It is referred as “frame tear” problem. A solution to solve the “frame tear” problem adapted in the prior art is to drop or to repeat the input image frames/fields by the frame buffer. However, such a solution would generate objectionable temporal distortions in the output image frames/fields. This is not acceptable for high-quality display apparatuses.
If the display apparatus can lock the output frame/field rate to the input frame/field rate, there are significant advantages because image fields/frames no longer need to be repeated or dropped, and the aforementioned temporal distortion problem in the displaying sequence for the image frames/fields can be eliminated.
Furthermore, in case the display apparatus has different input and output frame/field rates, if we can also lock the output frame/field rate to a fractional multiple of input frame/field rate, the “frame tear” problem can be avoid and the frame repeating and dropping will be reduced. The frame repeating and dropping will be periodic and predictable.
Therefore, one objective of the present invention is to provide a method and corresponding apparatus for solving the above-mentioned problems.